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ements  of 
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Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/elementsofmilitaOObarnrich 


ELEMENTS  of 
MILITARY  SKETCHING 

ARRANGED  FOR  USE  OF  THE  ORGANIZED 
MILITIA  OF  VERMONT 


By 

1st  Lieutenant  John  B.  Barnes 

Fifth  U.  S.  Infantry 


Copies  may^be  obtained  through  The  U.  S.  Infantry 

Association,  Washington,  D.  C,  at  fifty  cents  per  copy. 

Special  price  if  ordered  in  quantities. 


Copyrighted  1913 

by 

JOHN    B.    BARNES 


-3i 


PREFACE. 

The  diagrams  herein  were  executed  by  Sergeant  W.  Weiden- 
bach,  Company  "K",  5th  Infantry,  to  whom  credit  is  also  given  for 
valuable  assistance  in  originating  and  preparing  the  text. 

The  publication  of  this  pamphlet  was  undertaken  with  a  view 
of  supplying  a  simple  and  short  treatise  devoted  exclusively  to 
the  important  subject  of  Military  Sketching.  While  intended,  pri- 
marily, for  the  use  of  the  Organized  Militia  of  Vermont,  it  is 
thought  that  it  may  be  of  value  to  the  militia  of  other  states. 


281998 


Elements  of  Military  Sketching. 
MAP  SCALES. 

1.  A  map  is  a  graphical  representation  of  a  portion  of  the 
surface  of  the  earth.  A  7nap  is  made  with  the  proper  survey 
equipment  and  is  supposed  to  be  accurate.  A  sketch  is  as  nearly 
an  accurate  map  as  can  be  made  by  field  drafting  with  the  time 
and  instruments  available,  and  frequently  with  restricted  recon- 
naissance. 

Distances  on  a  map  have  a  fixed  proportion  to  distances  on 
the  ground  represented. 

In  order  to  read  or  make  a  map  it  is,  therefore,  necessary  to 
know  the  proportion,  or  ratio,  existing  between  any  given  map 
distance  and  the  actual  ground  distance  represented  by  it.  This 
ratio  is  expressed  by  means  of  map  scales. 

The  principle  of  scaling  is  that  one  unit  of  any  length  on  the 
map  represents  a  certain  number  of  like  units  on  the  ground. 

2.  This  ratio  existing  between  map  distance  and  ground 
distance  may  be  expressed  in  three  ways : 

( 1 )  In  words  and  figures,  as :  3  inches  =  i  miles. 

(2)  By  what  is  known  as  ''representative  Fraction" — a 
fraction,  the  numerator  of  which  shows  units  of  length  on  the 
map,  while  the  denominator  shows  the  corresponding  distance 
on  the  ground,  thus: 

Representative  Fraction,  (R.  F.)      ,  means  that  one 

21120 

inch,  or  one  unit  of  any  measure  on  the  map,  represents  a  distance 

of  21 120  inches,  or  units  of  that  measure,  on  the  ground. 

If  the  scale  of  a  map  were  4  inches  to  the  mile,  then  4  inches 

(map)  would  represent  63360  inches  (mile)  on  the  ground, 

4       (map-dist.) 

or 

63360  (ground-dist.) 

As  the  R.  F.  is  usually  written  with  numerator  unity,  we  would 

have  : 

R.  F.  -^ —  =  R.  F. 


63360  •  15840 

Emphasis  is  laid  upon  the  fact  that  R.  F.  is  internation- 
ally used;  this  circumstance  enables  us  to  readily  determine  the 


ElvKMENTS   OF    MlUTARY    SkKTCHING. 


scale  of  foreign  maps  in  inches  to  the  mile. 

(3)     The  scale  may  be  represented  graphically. 

A  graphical  scale  is  a  plotted  line  of  certain  length  to 
represent  a  given  ground  distance. 

Instead  of  writing  3  inches  =  i  mile,  we  may  draw  a  line 
three  inches  in  length  and  mark  it  i  mile.  Subdivisions  of 
this  line  represent  shorter  distances  and  are  marked  with  their 
respective  values. 

The  scales  of  American  (military)  maps  are: 

I    inch    (approximately)    to   the  mile,   or   R.    F. 


62250 
(Geological  Survey  Maps)  : 

3  inches  to  the  mile,  or  R.  F. (Scale  generally  used 

21120 

for  road  sketches  and  area  maps). 

6  inches  to  the  mile,  R.  F. (Scale  used  for  posi- 

10560 

tion  sketches.) 

12  inches  to  the  mile,  R.  F.  (Scale  used  for  forti- 

5280 

fication-plans,  war  game  maps,  etc.) 

Less  frequently  used  are  the  scales  2  inches  to  the  mile, 

I  I 

(R.  F. )  and  4  inches  to  the  mile,  (R.  F.    -). 

31680^  15840^ 

Construction  of  Graphicai.  Scai.es:    A  first  requirement 
in  map-making  or  map-reading  is  a  knowledge  of  scales.  Assume 

I 

that  a  map  has  R.  F. (3  in.  =  i  mile)  but  no  graphical 

21 120 

scale.  In  order  to  measure  off  any  definite  distance  on  the  map 
it  is  necessary  to  have  a  graphical  scale  of  3  in.  to  the  mile.  This 
scale  may  be  constructed  as  follows :  Draw  a  line  3  inches  long ; 
this  line,  representing  one  mile,  should  be  divided  into  1760  equal 
parts — each  part  representing  i  yard — but  as  such  division  can 


Elements  of  Military  Sketching. 


scarcely  be  made  without  special  instruments,  a  division  into 
17  6  parts  is  sufficient.  Each  subdivision  then  represents  100 
yards  ground-distance. 

In  constructing  this,  or  any  scale,  a  simple  method,  based 
upon  a  principle  of  plane-geometry  can  be  advantageously  follow- 
ed, viz: 

"If  an  angle  is  cut  by  a  series  of  parallels,  the  correspond- 
ing   segments    of    the    legs    of    the    angle    are    proportional." 

The  angle  B-A-C  is  cut  by  parallels;  thus  proportional  di- 
visions are  produced  on  both  legs  of  the  angle.     (Diagram  i). 

In  Diagram  la,  A-B  is  three  inches,  the  length  of  the  de- 
sired scale.  To  divide  A-B,  a  fixed  line,  into  17  ^  parts,  we 
simply  divide  A-C,  a  line  of  indefinite  length,  into  17  ^  parts, 
and  draw  parallels  through  the  division-marks  on  A-C  to  A-B. 

The  advantage  of  this  method  is  that  the  divisions  on  A-C 
can  be  of  any  convenient  length. 


EXAMPLES. 

Let  us  assume  the  scale  of  a  map  to  be  4  inches  to  the  mile, 

I 

(R.  F. ).     A  graphical  scale  is  desired. 

15840 

We  know  that  four  inches  represent  1760  yards. 
Select  a  more  convenient  number  of  yards  as  1000,  1600,  2000, 
etc.     We   can    solve   the   problem   by   proportion;    if   4   inches 
represent  1760  yards,  how  many  inches  represent  1000  yards? 

4  :  1760  :  :  X  :  1000  .      x  =  2.27. 

A  line  2.27  inches  in  length  is  drawn  and  divided  into 
equal  parts,  using  parallels  as  in  Diagrams  i  and  2. 

In  this  case  A-C  may  be  2y2^^  long.  Divide  A-C  into  ^/^  inch 
lengths  from  your  ruler  and  draw  parallels  from  these  points 
through  A-B.  A-B  is  then  divided  into  200  yard  lengths.  By 
estimation,  or  parallels,  subdivide  the  left  extension  to  read  small- 
er distances,  and  erase  line  A-C  and  parallels. 

Similiar  proportions  can  be  formed  with  any  convenient 
number  of  yards  as  given  ground-distances. 

The  scale  can  also  be  computed  as  follows : 


Elements  of  Military  Sketching. 


R.  F. that  is,  3  inches  =  i  mile  (1760  yards). 

21120 

1760 

I  inch  = =  586  +  yards. 

3 
A  graphical  scale  3  or  4  inches  long  is  desired. 
Select  a  convenient  number,  as  2000  yards. 
If  586  yards  are  represented  by  i  inch,  how  many  inches 
represent  2000  yards  ? 

2000 

— —=  34  inches. 
586 

4.  The  scale  reading  yards,  meters,  miles,  etc.,  usually  found 
on  a  completed  map  is  called  "reading-scale."  When  making  a 
map,  however,  a  so-called  "working-scale"  is  necessary.  In  mak- 
ing military  maps,  particularly  road  or  position  sketches,  the 
distances  on  the  ground  may  be  measured  by  pacing,  taking  the 
time  of  a  horse's  trot,  counting  telegj-aph-poles  with  reference  to 
their  interval,  counting  revolutions  of  a  wheel,  by  speedometer, 
odometer,  etc.  In  any  case  it  will  be  necessary  to  have  a  "work- 
ing-scale"— ^that  is,  a  scale  of  the  units  employed  in  measuring  the 
distances. 

The  units  of  the  ''reading  scale"  have  a  fixed  and  standard 
value  such  as  yards,  meters,  miles,  etc.,  while  the  units  of  any 
"working-scale"  used  in  making  a  map  depend  upon  the  individual 
and  the  means  at  hand  for  measuring  distances.  The  working 
scale  does  not  appear  on  the  completed  map. 

It  is  desired  to  make  a  road  sketch  3  inches  to  the  mile, 
distance  measured  by  pacing.  Assume  the  stride  of  the  mapper 
to  be  60  inches.  He  will  cover  100  yards  with  60  strides 
To  construct  the  working-scale,  we  use  the  same  method  em- 
ployed in  constructing  a  reading-scale,  but  changing  the  value 
of  the  scale-divisions  as  expressed  in  yards  to  the  corresponding 
number  as  expressed  in  strides  or  paces,  thus ;  100  yards  =  60 
strides.  120  strides  =  200  yards,  etc.  (It  is  advantageous  to 
combine  the  working-scale  with  reading  scale,  as  in  Diagram  3.) 

This  scale  would  usually  be  computed  as  follows : 

I  stride  =  60  inches ; 1  =  1056  strides  to 

60 

the  mile,  hence  3  inches  represent  1056  strides. 


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DiAQ.    5. 


Elements  of  Military  Sketching. 


3  :  1056  :  :  X  :  1000  .      x  =  2.84". 

Suppose  by  actual  experiment  over  a  measured  course,  a 
horse  has  been  found  to  trot  a  mile  in  7  min.  40  sec.  Then  7  % 
min.  =  1760  yards.  We  desire  to  make  a  working  scale  3"  to  the 
mile.  Take  10  min.  as  a  convenient  number.  Then  S  '  7  %  •  * 
X  :  10.  X  ^  S-Q"-  Construct  a  scale  3.9  inches  long  divided  to 
read  the  fraction  of  a  minute  desired. 

As  these  data  vary  with  the  individual  and  the  means  used  it 
is,  therefore,  necessary  to  determine  carefully  the  length  of  the 
measuring  unit  before  making  the  working  scale. 

When  preparing  a  working-scale  for  pacing,  much  atten- 
tion should  be  given  to  determining  correctly  the  length  of  the 
pace  in  inches.  In  testing  the  number  of  paces  over  a  measured 
course,  the  gait  and  length  of  step  should  be  natural.  A  mea- 
sured course  of  100  yards  may  suffice,  but  a  mile  course  over  an 
undulating  road  will  give  more  accurate  results.  The  mean  of 
several  trials  will  give  still  greater  accuracy. 

The  same  applies  to  a  scale  of  minutes.  By  careful  tests  it 
must  be  ascertained  how  many  minutes  a  horse  requires  to  cover 
a  given  distance  at  a  trot  or  walk. 

The  average  horse  covers  one  mile  in  8  minutes  at  a  trot^ 
and  in  16  minutes  at  a  walk.     (Diagram  4). 

(Note) — Prepared  Working  Scales  of  any  length  of  pace, 
or  minutes  of  a  horse  trotting  can  be  obtained  at  a  nominal  cost 
from  the  Book  Department,  Service  Schools,  Ft.  Leavenworth, 
Kans. 

CONVENTIONAL  SIGNS. 

5.  The  purpose  of  a  military  map  is  the  graphical  represent- 
ation of  ground  with  constant  reference  to  probable  military  use. 
It  should,  therefore,  not  only  be  true  in  regard  to  distances  and 
directions,  but  should  also  give  a  comprehensive  picture  of  the 
condition  of  the  ground  as  to  cultivation,  geological  formation, 
and  other  features  of  military  interest,  as  railroads,  telegraph 
lines,  bridges,  etc.  Consequently  it  has  been  necessary  to  invent 
characteristic  graphic  signs,  (called  Conventional  Signs),  to  re- 
present all  objects  of  military  importance,  and  the  form  of 
the  ground  itself. 

The  more  common  conventional  signs  used  in  military  topo- 
graphy are  given  in  Diagram  5. 


10 


Elements  oe  Military  Sketching. 


Many  of  these  conventional  signs  are  used  only  in  elaborate 
topographical  work.  For  hasty  sketching,  (road  or  position- 
sketches),  the  simplified  conventional  signs  as  given  on  pages 
209  and  210,  Appendix  C,  Field-Service  Regulations  1910,  an- 
swer all  purposes.  Grass,  trees,  cultivated  land,  woods,  etc.,  are 
therein  more  simply  represented  by  drawing  the  outline  of  the 
particular  feature  and  placing  inside  the  appropriate  symbol  or 
letter,  (Diagram  5a).  This  method  is  recommended  in  all  re- 
connaissance or  hasty  sketching. 

Diagram  6  indicates  the  character  of  stream,  span  and  con- 
struction of  the  bridge.  (Stream  20  feet  wide,  3  feet  deep  and 
fordable.  Wooden  queenpost  post  bridge  35  feet  long,  14  feet 
wide  and  10  feet  above  the  water.) 

"The  following  abbreviations  are  authorized  for  use  on  field 
maps  and  sketches.  When  these  words  are  used  they  must  be 
written  in  full  or  abbreviated  as  shown.  The  abbreviations  must 
not  be  used  for  words  other  than  those  in  the  table.  Words  not 
in  the  table  are  not  as  a  rule  abbreviated".    (F.  S.  R.  1910). 


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postoffice 

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bottom 

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creek 

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river 

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round  house 

d. 

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railroad 

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east 

S. 

south 

f. 

fordable 

s. 

steel 

gir. 

girder 

S.H. 

school  house 

G.M. 

gristmill 

S.M. 

saw  mill 

i. 

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station 

I. 

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stone 

jc. 

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str. 

stream 

kp.    • 

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tres. 

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lake 

tr. 

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north 

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water  works 

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Elements  of  Military  Sketching.  ii 


ORIENTATION. 

6.  Orientation  is  placing  the  map  in  its  true  relation  to 
the  ground  represented ;  in  general,  the  location  of  any  point  in 
relation  to  the  north  and  south  of  the  map  as  determined  by  the 
magnetic  needle. 

As  a  rule  maps  have  a  north  and  south  line. 

It  should  be  known,  however,  that  the  compass-needle  does 
not  in  all  localities  point  true  north,  but  usually  varies  several 
degrees  East  or  West.  This  is  called  ''magnetic  variation" 
(deviation,  declination). 

Consequently  there  may  be  two  direction-lines  on  a  map,  the 
"true"  north  and  the  ''magnetic"  north.     (Diagram  8.) 

In  this  instance  the  magnetic  needle  has  a  deviation  of  14' 
26'  30"  East  from  the  true  north  or  true  meridian. 

The  true  meridian  lies  in  the  direction  of  the  North  Pole. 
It  is  a  datum-line,  a  constant,  whereas  the  N.  &  S.  Line  as  indi- 
cated by  the  compass-needle  is  variable  because  of  magnetic 
influences,  depending  on  the  locality  and  the  time.  The  magnetic 
meridian  is  usually  represented  by  a  spear,  one  side  of  the  point 
of  which  is  missing,  while  the  true  meridian  is  represented  by 
the  spear  with  point  completed. 

To  orient  oneself  it  is  only  necessary  to  bring  the  magnetic 
•  North  of  the  map  to  point  in  the  same  direction  as  the  north  end 
of  the  compass  needle  and  then  the  bearings  of  lines  on  the  map 
and  corresponding  lines  on  the  ground  will  be  the  same.  That 
is,  lines  on  the  map  will  be  parallel  to  the  lines  on  the  ground 
represented. 

In  Diagram  9,  a  road  A-B  is  plotted  on  the  map ;  the  magnetic 
N.  and  S.  line  is  indicated.  You  are  standing  on  the  road  and 
desire  to  orient  the  map.  Place  the  compass  on  the  map  so  that 
the  line  marked  N.  and  S.  on  the  dial  is  parallel  to  and  agrees  with 
the  direction  line  on  the  map.  Turn  the  map  (without  disturbing 
the  position,  on  the  map,  of  the  compass  box)  until  the  north  end 
of  the  needle  points  towards  N.  The  map  is  now  oriented,  and 
A-B  on  the  map  has  the  same  direction  as  the  road  on  the  ground. 

Diagram  10  illustrates,  that,  if  the  compass-ntedle  and  the 
direction  line  on  the  map  do  not  coincide — no  coincidence  in  the 
direction  of  the  roads  is  obtained,  and  the  map  is  not  oriented. 


12  ^  Elements  of  Military  Sketching. 

The  true  meridian  can  be  determined  by  means  of  a 
watch,  as  follows :  Place  the  watch  face  up  with  the  hour  hand 
pointed  towards  the  sun.  A  line  midway  between  the  hour  hand 
and  the  number  XII  will  lie  in  the  direction  of  the  true  meridian. 
The  north  and  south  ends  of  this  line  are  evident  from  the  hour 
of  the  day  and  the  position  of  the  sun.  (To  bring  the  hour  hand 
in  the  direction  of  the  sun,  hold  a  straw  perpendicularly  between 
the  sun  and  the  watch,  and  bring  the  hour  hand  in  its  shadow.) 
(Diagram  ii.) 

With  the  true  meridian  on  the  map  the  magnetic  declina- 
tion of  the  compass-needle  can  be  ascertained  as  follows :  Bring 
the  N.  &  S.  line  as  indicated  on  the  compass-face  to  coin- 
cide with  the  true  meridian,  map  oriented.  The  compass-needle 
will  then  be  found  to  vary  several  degrees  to  the  East  or  West 
of  the  true  meridian  line.  This  deviation  varies  from  o°  to  25° 
in  the  United  States. 


RESECTION  AND  INTERSECTION. 

7.  Resection  is  a  method  of  locating  unknown  points  by 
taking  the  bearings  of  two  or  more  given  points.     (Diagram  12). 

We  think  we  are  on  some  point  of  the  road  A-B,  and  we 
want  to  locate  our  exact  position.  Facing  B,  we  have  two 
distinct  landmarks  on  our  left,  the  top  of  hill  (X)  and  the 
cottage  in  front  of  the  pine-wood,  both  of  which  we  can  locate 
on  our  map  and  identify  on  the  ground.  Keeping  the  map 
oriented,  we  sight  towards  the  hill  until  a  point  (X  on  the  map) 
and  the  actual  top  of  the  hill  are  in  the  same  line  of  sight. 
We  plot  the  line  of  sight  by  drawing  a  back  line  through 
X  across  the  road.  This  line,  obtained  through  connecting  three 
points  (top  of  hill,  X,  ourselves),  would  sufficiently  locate  our 
place  on  the  map  if  we  were  sure  to  be  on  the  road  A-B.  In 
order  to  ascertain  this,  a  second  similar  sight  is  taken  on  point 
Y  (cottage)  and  the  line  of  sight  plotted  in  the  same  manner. 
Both  lines  of  sight  will  cross  at  a  certain  point.  The  point 
of  intersection  locates  our  exact  place  on  the  map,  as  we 
are  on  the  line  S-X,  and  also  on  the  line  S-cottage. 

8.  Intersection  is  the   same  principle  applied  to  locate 


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DiAG.    17. 


Elements  of  Miutary  Sketching.  13 

and  plot  points  situated  off  the  course  of  the  topographer.  (Dia- 
grams 13  and  14).  Intersection  is  used  in  both  map  reading  and 
map  making. 

You  are  on  the  road  B-A,  (Diagram  14),  and  desire  to  plot 
an  object  several  hundred  yards  off  the  road.  Stop  at  any  point  of 
the  road  (as  i),  orient  the  sketch  and  sight  towards  this  objeci, 
plotting  the  line  of  sight  by  drawing  an  indefinite  straight 
line  from  your  position  towards  the  object.  After  having  march- 
ed a  certain  distance  (as  at  2)  a  second  sight  is  taken  and  the 
line  of  sight  plotted  in  the  same  manner.  This  will  intersect  the 
first  line.  The  point  of  intersection  locates  the  object.  This 
method  is  very  accurate  provided  the  base-line  is  correct;  care 
should,  therefore,  be  taken  to  measure  and  plot  correctly  the 
distance  between  the  first  point  of  sighting  and  the  second. 
The  smaller  the  angle  at  X  the  greater  will  be  the  chance  of  error. 
Therefore,  this  angle  should  approach  a  right  angle  when  prac- 
ticable. 

SKETCHING  IMPLEMENTS. 

9.        Cavalry        A  drawing  board  with  a  compass  set  in.     The 
Sketching  Case  paper  is  tightly  rolled  over  two  metallic  rollers 

(Diag.  15.)  on  opposite  ends  of  the  board.  An  arm  with 
a  brass  scale  (3  inches  to  the  mile)  is  fastened 
to  it,  freely  moving  around  a  pivot.  This  arm 
with  the  graduations  on  the  bottom  of  the 
board  is  also  used  for  measuring  slopes  in 
the  manner  described  below,  the  movable  ruler 
taking  the  place  of  the  pendulum.  The  grad- 
uations are  for  slopes  of  from  1°  to  20°. 
Plane- Table      A  good  device  for  mapping,  is  a  simple  plane- 

(Diag.  16.)  /a&/^,  (a  smooth  board  about  16  inches  square) 
with  a  compass  set  in.  Slopes  are  measured 
with  some  form  of  hand  level  or  slope  board, 
and  in  taking  bearings  the  board  is  kept  orient- 
ed by  means  of  the  compass  or  by  "backsight- 
ing."  The  paper  is  held  in  place  by  thumb  tacks. 
The  board  is  fastened  to  a  tripod.  A  modifi- 
cation of  this  device,  always  available,  is  a 
smooth    board    or    stiff    card    board    about 


14  Elements  of  Military  Sketching. 

I2"xi2'',  without  tripod,  and  a  loose  box  com- 
pass. A  ruler,  paper,  thumb  tacks,  pencil  and 
scales  complete  the  equipment.  Under  service 
conditions,  hasty  sketching  will  usually  be  done 
with   such   an   improvised   plane  table.     Any 
paper    that    will    stand    erasing    is    suitable; 
tracing  paper  is  very  good.     HH  to  HHHH 
pencils  are  generally  used,  except  with  tracing 
paper  when  B  or  HB  pencils  are  preferable. 
When  sketching  by  pacing,  a  pace  tally  for 
registering    paces    or    strides    is    convenient. 
When  sketching  mounted,  a  stop  watch  should 
be  used. 
Slope-Board.      The  slope-board  is  a  simple  device  for  mea- 
(Diag.   17.         suring  degrees  of  slope.     The  essential  part 
18  and  i8a.)       of  the  slope-board  is  a  pendulum  registering 
every  change  of  level.     It  is  constructed  as 
follows : 
Suspend  a  small  weight  on  a  string,  thus  forming  a  crude 
plumb  line  and  bob.     Attach  the  free  end  of  the  string  to  the 
middle  point  of  one  edge  of  a  rectangular  board   (the  drawing 
board.)     If  this  edge  of  the  board  be  kept  uppermost  and  level 
the  plumb  line,  or  pendulum,  will  hang  perpendicularly,  and  will 
thus  bisect  the  board.     Mark  a  point  O  on  this  bisecting   line 
near  the  bottom.     If  the  level  of  the  upper  edge  of  the  board  is 
disturbed  by  sighting,  the  pendulum  will  appear  to  move  forward 
or  back  of  O.     This  apparent  course  of  the  pendulum  (A-B,  Dia- 
grams 17  and  18)   is  a  sector  that  can  be  divided  into  degrees. 
In  the  diagrams,  from  C  to  the  line  A-B  is    assumed  to  be  5,  7 
inches,  and  the  divisions  on  A-B  are  i-io  inch  apart.     Each  divi- 
sion on  a  slope  board  so  constructed  will  read  an  angle  of  1°. 

To  use,  sight  at  the  object  along  the  edge  (top)  of  the  board, 
at  an  elevation  on  the  object  of  about  5  ft.  (height  of  the  eye)  and 
read  the  degrees  registered  by  the  pendulum.  (Diagram  i8a.) 
Forward  is  a  minus  and  backward  a  plus  elevation.  It  is  usually 
more  convenient  to  use  both  hands  in  sighting  and  to  hold  the 
plumb  line  against  the  board  with  the  left  thumb  when  it  is  turned 
to  be  read.  The  slope-board  should  be  constructed  on  the  reverse 
side  of  the  drawing  board. 


Elements  of  Military  Sketching. 


The  Locaters  Hand  Level  is  a  practical  and  handy  slope 
measuring  instrument  especially  designed  for  use  of  sketchers. 
(Diagram  i8b).  It  can  be  used  as  a  hand  level  and  clinometer  or 
gradienter  at  a  single  observation.  When  the  tube  is  level  an  ob- 
ject on  a  line  with  the  base  of  the  locaters'  level  object  glass  is — 5°. 
Thus,  in  the  figure,  the  observer  sights  the  top  of  the  barn,  as  0° 
(level)  and  at  the  same  time  can  see  that  the  eaves  of  the  barn 
are — 1°,  and  the  base  of  the  barn  is — 3°,  being  on  a  line  with  the 
third  graduation  below  the  center,  observing  the  bridge — 5°, 
which  is  the  limit  of  the  field.  But  an  object  outside  the  neld  can 
still  be  measured  in  vertical  angle.  To  measure  the  vertical  angle 
to  the  foot  of  the  tree : — disregard  the  bubble,  hold  hand  level 
so  that  an  object  which  is — 5°  (as  the  bridge)  is  seen  at  the 
top  of  the  object  glass,  and  observe  the  number  of  degrees  between 
the  bridge  and  the  foot  of  the  tree;  in  this  case  it  is  the  whole 
field  of  the  tube  or  10°,  hence  the  base  of  the  tree  is — 15°. 

The  locaters'  level  is  made  with  three  separate  graduations : 
degrees,  grade  in  per  cent,  and  in  mils  (for  artillery.)  (For  sale 
by  the  U.  S.  Cavalry  Association,  Fort  Leavenworth,  Kans). 

Scale  of  the  units  of  measure : — This  scale  if  not  prepared 
by  the  individual,  can  usually  be  purchased  at  a  trifling  cost.  (If 
pacing  a  scale  of  strides  should  be  used.) 

Scale  of  M.  D. 

A  Triangular  Ruler,  with  the  scales  pasted  on  it,  facili- 
tates plotting  and  sighting. 

Box-CoMPASS.  (Diagram  19) — A  simple  box-compass  is 
preferable  for  the  beginner.  The  graduations  may  be  clockwise 
from  0°  to  360°,  contra-clockwise  from  360"  to  o",  or  in 
quadrants  from  0°  to  90°.  A  compass  graduated  contra-clockwise 
(i.  e.  in  reverse  order  of  the  graduations  on  the  face  of  a  clock) 
is  the  better  as  it  reduces  chances  of  error  in  plotting  with  a 
protractor. 

Attention  is  invited  to  the  arrangement  of  the  cardinal- 
points  on  the  dial  of  the  box-compass  in  Diagram  20.  Note  that 
E  is  to  the  left  of  N.  This  reversion  of  East  and  West  has  been 
made  purposely.  A  compass  with  a  dial  so  lettered  is  more  con- 
venient for  reading  directions.  As  an  example,  let  us  assume 
the  course  of  a  road  to  be  North  and  then  turn  to  North- West. 
In  the  first  instance  the  position  of  the  magnetic  needle  will  be  as 


i6  Elements  oe  Military  Sketching. 

in  Diagram  21.  The  road  then  turns  to  N-W  (Diagram  22.)  We 
sight  along  the  edge  of  the  compass-box  in  the  new  direction.  The 
needle  leaves  N  and  moves  toward  W  (on  the  dial).     We  take 

the  reading  from  N  to  the  needle, degrees  N-W. 

The  change  of  direction  has  really  been  N  -  W.  If  a 
reversion  of  the  cardinal-points  E  and  W  had  not  been  ;made, 
the  reading  would  obviously  be  more  difficult,  and  it  is  very  pro- 
bable that  the  sketcher,  while  working  rapidly,  would  have  read — 
degrees  N-E  if  this  reversion  of  E  and  W  were  not  shown. 

ROAD  sketching — WITH  A  DRAWING  BOARD   ( PLANE  TABLE) 
OR  SKETCHING  CASE.       (DIAGRAM  23.) 

10.  The  starting  point  is  marked  (i),  [station  one].  With 
the  beginner  all  changes  of  direction  should  be  similarly  marked ; 
with  more  practice  all  such  data  can  be  omitted. 

The  needle  of  the  compass  is  allowed  to  settle  over  the  North 
and  South  line  indicated  by  letters  N  and  S  on  the  compass-face. 
(If  a  drawing  board  with  no  compass  set  in  is  being  used,  lay  a 
box-compass  on  the  board)  ;  hold  the  board  steadily  so  as  to  allow 
the  needle  the  least  possible  swing.  (To  be  exact,  the  needle  should 
be  absolutely  immobile ;  this,  however,  is  hardly  to  be  accomplished 
without  a  tripod,  unless  the  board  is  laid  on  the  ground). 

The  needle  being  settled,  draw  a  line  parallel  to  it.  Mark  the 
north  end. 

This  line  is  the  N.  &  S.  line  (meridian)  of  the  map,  and 
with  reference  to  this  line  all  further  directions  are  determined. 

Plot  the  starting  point  on  the  paper.  Keeping  the  needle  pa- 
rallel with  the  plotted  map-meridian  (N  &  S.  Line),  sight  along 
the  ruler  in  the  direction  of  the  road  by  moving  the  ruler, 
[using  station  ( i )  as  a  pivot] ,  until  it  and  the  road  are  in  the  same 
line  of  sight.  Draw  an  indefinite  line  forward  along  the  ruler 
while  holding  it  firmly  in  place  with  the  other  hand. 

Step  off  with  the  right  foot,  counting  the  strides,  and  plotting 
the  distances  to  scale. 

When  a  change  of  direction  occurs,  stop,  orient  the  board, 
and  plot  the  new  direction  line. 

Observe  carefully  the  "lay"  of  the  ground.  Plot  houses, 
woods,  telegraph-lines,  etc.,  etc. 


LOCATERS  HAND  LEVEL 


^ 


Brid9fc 


This  15° reading  is  takan 
disregarding  the  bobble 


DiAO    18b. 


DiAG.  19. 


so  o 


DiAG.    20. 


DiAG.  24. 


Elements  of  Military  Sketching.  17 

It  is  customary  to  take  in  all  military  details  within  three  hun- 
dred yards  of  the  road  traversed,  and  conspicuous  landmarks, 
high  hills,  etc.,  by  intersection  or  estimation  to  greater  distances, 
depending  on  the  object  of  the  sketch.  Cuts,  fills,  railroad 
embankments,  etc.,  should  never  be  overlooked  as  they  may  have 
tactical  value. 

In  traversing  it  is  not  necessary  to  halt  and  plot  each 
feature  as  it  is  reached.  A  note  can  be  made  of  the  distances 
and  the  features  "plotted  in"  when  it  becomes  necessary  to  halt 
on  account  of  a  distinct  change  of  direction. 

For  example,  starting  from  (i),  carefully  orient  your  board, 
draw  an  indefinite  straight  line  toward  (2)  and  then  pace 
(or  otherwise  measure)  the  distance  without  halting  to  plot,  hav- 
ing made  notes  en  route  of  the  location  of  the  woods  to  the  right 
and  left;  at  (2)  lay  off  the  distances  by  scale  and  complete  the 
sketching  to  that  point.  Then  stand  in  the  middle  of  the  road 
(board  oriented)  and  sight  towards  (4)  ;  at  (3)  it  will  be  necessary 
to  halt  to  get  the  direction  of  the  side-road.  Now  pace  to  (4)  and 
in  laying  off  this  distance,  lay  off  the  whole  number  of  strides 
from  (2).  If,  for  example,  you  have  had  260  strides  from  (2) 
to  (3)  and  230  strides  from  (3)  to  (4),  in  plotting  (4)  lay 
off  the  whole  distance  490  strides  from  (2).  This  method 
lessens  the  accumulation  of  errors  arising  in  taking  distances 
from  your  scale. 

At  (4)  sight  towards  (6).  Halt  at  the  stream  to  get  its 
direction,  and  the  data  for  the  bridge.  Continue  in  this  manner. 
[Contouring  methods  will  be  explained  later.] 

If  taking  strides,  count  every  time  the  left  foot  strikes  the 
ground,  and  be  careful  that  hundreds  are  not  gained  or  lost. 

During  each  sight  the  board  must  be  kept  oriented.  This 
may  be  done  by  means  of  the  compass,  or  by  backsighting  on  the 
last  station. 

Telephone — or  telegraph — wires  or  other  metal  objects,  de- 
flect the  compass  needle,  and  this  cause  of  inaccuracy  must  be 
guarded  against  when  sighting  or  orienting  the  board. 

The  hill  320  is  located  by  intersection.  Sight  on  the 
hill  from  station  (6),  plotting  the  line  of  sight;  take  a  second 
sight  from  (7)  or  (8)  or  (9)  and  plot  the  line  of  sight.     The 


i8^  Elements  of  Military  Sketching. 

point  of  intersection  of  the  two  lines  of  sight  locates  the  object  on 
your  paper. 

II.  In  road  sketching,  it  often  happens  that  a  change  of 
direction  causes  the  plotting  to  run  off  the  paper.  (Diagram  25.) 
Draw  a  cross-line  at  right  angles  to  the  edge  of  the  paper, 
cutting  the  point  where  the  plotting  runs  off  (A-B,  Diagram 
26.)  By  plotting  the  angle  X'  on  B-A,  we  would  have  the 
direction  of  the  road,  because  X'  and  X  are  opposite  angles  and 
equal.  The  usual  way,  however,  is  to  select  the  point  A'  (which  is 
the  same  point  on  the  road  as  A)  at  any  convenient  place  on  the 
paper  with  a  view  of  continuing  the  sketch;  then  plot  a  new 
north  and  south  line  and  begin  a  new  sketch.  If  the  general 
direction  of  the  route  is  known,  the  starting  point  on  the  paper 
should  be  selected  with  a  view  of  getting  as  much  of  the  sketch 
as  possible  on  that  sheet.  To  this  end  the  board  should  be  so 
oriented  that  the  longer  axes  of  the  paper  will  be  in  the  general 
direction  of  the  route  to  be  sketched. 

We  may  thus  have  a  series  of  sections  of  the  same  route. 
Number  these  sections  in  sequence.  They  may  be  put  together 
by  pasting  the  several  sections  together,  or  on  a  new  sheet  in  their 
proper  order. 

In  diagram  26,  the  sketch  (2)  is  a  continuation  of  sketch 
(i).  When  putting  the  sections  together  point  A'  is  laid  on 
point  A,  care  being  taken  to  keep  the  meridians  of  all  sections 
parallel. 

After  completing  the  sketch  a  simple  "legend"  or  title, 
is  added  to  the  plotting,  describing  route,  scale,  vertical  interval, 
etc.,  etc.  (Diagram  24).  Written  titles  will  answer  all  purposes, 
though  printing  is  generally  used.  The  Reinhardt  system  of 
printing,  as  in  the  diagram,  is  most  easily  acquired. 

All  officers  and  non-commissioned  officers  should  be  capable 
of  readily  making  a  hasty  reconnaissance  or  outpost  sketch,  as 
such  sketch  accompanied  by  a  written  report  will  generally  give 
more  complete  and  clear  information  than  can  be  conveyed  by  any 
written  report  alone.  As  the  proximity  of  the  enemy  may  pre- 
vent traversing,  it  will  sometimes  be  necessary  to  make  such  a 
sketch  from  one  station  and  with  only  a  note  book  and  pencil. 
The  report  to  accompany  the  sketch  (Diagram  7)  might  be  about 
as  follows: 


< 


DiAG.  28. 


DiAG.  29. 


DiAG.   31. 


DiAG.  32. 


■o 


P  r- 


Elements  of  Military  Sketching.  19 

"Station  (i)  and  (2)  are  joined  by  an  improved  road;  the 
bridge  is  guarded  by  a  detachment  of  hostile  troops;  hostile 
sentries  are  posted  along  the  edge  of  the  wood  on  the  north 
side  of  the  river.  The  wood  is  thick  and  reaches  as  far  as  the 
village  of  Boxford.  A  body  of  our 'troops  could  easily  win  the 
fire-protection  of  the  houses,  which  are  generally  of  brick. 
The  cultivated  ground  to  the  front  affords  no  cover.  Natives  state 
that  the  river  is  fordable  just  west  of  the  bridge." 

CONTOURS  AND  CONTOURING. 

12.  Contours  are  imaginary  horizontal  lines  circumscrib- 
ing elevations  (or  depressions)  on  the  Earth's  surface  at  equal 
vertical  distances.  The  theory  and  application  of  contouring 
methods  thus  offer  a  means  of  representing,  graphically,  the  forms 
of  the  ground. 

The  map-scale  deals  with  horizontal  distances  (areas),  while 
the  contour  deals  with  vertical  distances,  i.  e.,  height  or  depth. 

Before  the  principles  of  contouring  were  applied,  ground 
forms  were  represented  by  means  of  "Hachures" — parallel  dashes 
in  the  direction  of  the  slope,  shading-work  with  an  effort  to  give 
plastic  impression.     (Diagram  27). 

This  method  is  not  accurate  and  is  rendered  obsolete  through 
the  evident  superiority  of  contouring. 

How  can  the  hill  X  be  represented  on  a  map?  (Diagram  28) 

In  Diagram  29,  a  series  of  horizontal  planes  (with  equal 
vertical  distances)  are  passed  through  the  hill  X.  (See  diagram 
32.) 

It  is  apparent  that  the  edge  (a  Hne)  of  each  plane  follows 
the  form  of  the  ground.     (Diagram  30,  upper  half.) 

These  lines  are  called  "CONTOURS",  and  the  sum  of  their 
vertical  distances  is  the  total  height  of  the  elevation. 

The  lines  are  plotted  by  "horizontal  projection;"  that  is,  if 
perpendiculars  are  dropped  from  points  along  the  edges  of  planes 
to  the  (lowest)  base-plane  (water  level)  and  the  projected  points 
on  the  base-plane  are  then  joined,  a  true  picture  of  the  correspond- 
ing plane  is  obtained.     (Diagram  30  lower  half). 

13.  By  comparing  the  lower  with  the  upper  half  (diagram 
30)  it  is  seen  that  the  plotted  contours  are  far  apart  along  the 


20  Ei.e:mi:nts  of  Military  Sketching. 

gradual  slope  D-E,  while  they  close  along  the  steeper  slope  F-E. 
The  location  of  these  contours  is  determined  from  the  relation  of 
ground  distance  to  degree  of  slope,  and  involves  a  consideration 
of  the  meaning  of  the  terms  Vertical  Interval,  and  Map 
Distance. 

Vertical  Interval  (V.  I.)  is  the  vertical  distance  (i.  e.  the 
difference  in  elevation)  between  adjacent  contour  planes.  In 
the  slope  represented  in  diagram  35,  the  contour  planes  passing 
through  the  points  A,  R,  C,  are  20  feet,  vertical  distance,  apart, 
(R-Q),  and  are  said  to  have  a  V.  I.  of  20  feet. 

The  actual  ground  distance  between  A,  and  the  first  contour 
point  is  represented  by  A-R.  A-Q  is  the  horizontal  projection 
of  this  ground  distance  and  is  called  Map  Distance  (M.  D.) 
when  plotted  to  scale  on  the  map.  Map  Distance  is,  therefore, 
the  plotted  horizontal  or  level  distance  between  adjacent  contours. 

In  diagram  35a,  A-D  and  A-C,  representing  slopes  of 
different  degrees,  have  the  same  horizontal  distance,  A-S.  Con- 
tours for  the  slope  A-D  would  be  plotted  on  the  map  at  W,  W,' 
W,"  W,'"  and  at  S,  while  contours  with  the  same  V.  I.  for  the 
slope  A-C  would  be  plotted  at  Q,  and  S  only.  The  total  horizontal 
distance  is  the  same  for  each  slope,  but  the  Map  Distances  be- 
tween contours  on  each  slope  are  in  reverse  proportion  to  the 
degrees  of  slope :  and, 

AW :  AQ  : :  angle  SAC :  Angle  SAD. 

It  is  sufficient  to  know  that  on  a  1°  slope  we  will  get 
an  elevation  of  one  foot  in  a  horizontal  distance  of  57.3 
feet.  Therefore,  we  would  get  an  elevation  of  20  feet  in  a 
horizontal  distance  of  1146  feet  (20x57.3),  and  on  a  5°  slope  we 
would  rise  20  feet  in  a  horizontal  distance  of  229.2  feet  (1146-^  5), 
etc. 

The  M.  D.  for  any  degree  of  slope  may  be  determined  by  the 

following  formula: 

V.I.X57.3 

M.  D.  = plotted  to  the  scale  of  the  map. 

Degree  of  slope. 

In   sketching,   where  time   and   instruments    for   measuring 

horizontal  distances  are  usually  not  available,  the  actual  ground 

distances  are  plotted  instead  of  the  horizontal  distances,  as  would 

obtain  in  a  survey. 


DiAG.  34. 


DiAG.  34a. 


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DiAG.  33. 


Elements  of  Miutary  Sketching.  21 

[Note :  Map  Distance  is  sometimes  referred  to  as  Horizontal 
Bquivalent  or  H.  E.] 

To  construct  a  scale  of  M.  D.,  plot  the  horizontal  distance 
for  the  different  degrees  of  slope  to  the  scale  of  the  map.  Dia- 
gram 36  shows  a  scale  of  M.  D.  for  the  map  scale  and  V.  I. 
indicated.  A  scale  %°  to  10°  will  usually  cover  all  cases.  The 
Book  Department,  Service  Schools,  Fort  Leavenworth,  Kans., 
supplies  a  "slope  card"  (Diagram  37)  giving  M.  D.  for 
slopes  from  %"  to  10°  for  maps  3,  6,  or  12  inches  to  the 
mile  with  corresponding  contour  intervals  of  20,  10  or  5  feet. 

15.  A  simple  demonstration  of  the  theory  of  contouring  is 
the  following:  Of  soft  material  (clay  or  sand)  form  a  small 
irregular  figure,  giving  it  the  shape  of  a  hill :     (Diagram  31). 

Pass  several  horizontal  planes  (pasteboard)  through  this 
figure,  carefully  preserving  an  equal  vertical  interval  between 
planes:     (Diagram  32.) 

Where  a  plane  passes  through  the  figure  by  outlining  its 
shape  with  a  pencil,  an  exact  plotting  of  the  form  of  the  figure 
at  this  particular  level  will  be  obtained:  (Diagram  32  a). 

File  these  planes  along  a  perpendicular  axis  (wooden-staff), 
preserving  the  original  vertical  interval  between  planes.  (Diagram 

33-) 

To  demonstrate  "horizontal  projection."  the  higher  planes 
are  moved  along  the  axis  to  the  lowest  plane.  (Diagram  34).  A 
true  map-picture  of  the  hill  is  thus  obtained. 

Diagram  34a  illustrates  the  manner  of  representing  some 
characteristic  ground  forms. 

16.  In  road  or  position  sketching  contours  are  located  and 
plotted  as  are  other  features,  slopes  being  measured  or  estimated, 
and  slope  card  or  scale  of  M.  D.  applied.  If  the  elevation  of  the 
starting  point  above  the  datum  or  sea  level,  is  not  known,  any 
elevation  for  the  point  may  be  assumed ;  further  changes  of  level 
are  relative  to  the  assumed  elevation  of  the  starting  point.  As 
a  matter  of  convenience,  any  assumed  elevation  should  be  some 
hundreds  of  feet  100,  500  or  1000,  etc.,  a  sufficient  elevation 
being  assumed  to  insure  having  no  contour  with  a  minus  designa- 
tion. For  example,  if  starting  a  sketch  with  an  assumed  elevation 
of  100  feet,  and  later  ground  is  encountered  with  an  elevation 
of  120  feet  less  than  the  starting  point,  it  would  be  necessary 


22     ^  Elements  of  Military  Sketching. 

to  number  this  lowest  point  (minus) — 20  feet.  This  could  have 
been  avoided  by  assuming  a  greater  elevation  at  the  starting  point, 
such  as  500  feet.  In  sketching  it  must  be  understood  that  the 
exact  determination  of  elevations  of  points  above  sea  level  is 
not  usually  essential,  but  that  the  value  of  contouring  is  in  show- 
ing on  the  map  the  relative  elevations  of  such  points. 

17.  In  Diagram  i8a  the  reading  of  the  slope  board  is  +  4." 
The  hill  is  then  said  to  have  a  slope  of  4° ;  traverse  (or  estimate) 
the  distance  between  points  of  sighting  and  the  top  of  the  hill, 
which  is  found  to  be  500  yards.  Plot  the  point  and  apply  the 
scale  of  M.  D.  (slope-card)  on  the  ray  to  the  hill  to  determine 
the  number  and  location  of  contours.  If  the  slope  is  not  uniform, 
the  number  of  contours  (height  of  the  hill)  remains  the  same 
of  course,  but  the  exact  location  of  the  contour  lines  must  be  de- 
termined by  estimation.  As  the  steepness  of  slope  varies  in  going 
from  the  sighting  position  to  the  top  of  the  hill,  the  M.  D.  between 
adjacent  contours  must  vary  accordingly. 

In  Diagrams  38  and  38a  a  road  (A-B)  passes  a  hill.  The 
highest  points  of  the  elevation  (x  and  y),  are  located  by  inter- 
section from  the  road.  As  the  road  is  being  traversed  it  is  not 
difficult  to  determine  the  lowest  points  of  the  hill,  that  is,  where 
the  slope  loses  itself  in  the  level  of  the  road.  Measure  the  slope  to 
y  and  to  x,  from  the  two  points.  Apply  the  scale  of  M.  D.  for  the 
determined  degrees  of  slope  along  the  plotted  intersecting  lines, — 
indicating  the  contour  points.  Plot  contours  through  these  points, 
tracing  their  intermediate  course  by  estimation. 

Points  C  and  D  may  also  be  located  by  intersection. 

In  order  to  contour  a  map  accurately,  precise  angle  measur- 
ing instruments  (as  a  transit  or  "Y"  level)  should  be  used.  Any 
other  method  will  be  more  or  less  inaccurate.  For  rapid  sketching, 
however,  with  an  allowable  error  of  5%,  a  hand  level,  slope  board, 
or  carefully  trained  estimation  will  answer  all  purposes. 


DiAG.  38. 


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DiAG.  36. 


Elements  of  Military  Sketching.  23 


POSITION  SKETCHING. 

18.  A  position  sketch  or  map,  differs  from  a  road  sketch  in 
that  some  complete  area  is  shown  instead  of  only  a  road 
and  the  features  near  it,  (Plates  A  and  B.) 

The  ordinary  military  map  is  an  example  of  a  position  map 
of  an  extended  area  made  with  accurate  instruments,  and 
involving  considerable  time  in  its  preparation.  Position  sketches 
must  usually  be  expeditiously  made  and  may  range  in  accuracy 
from  the  crudest  outpost  sketch  to  a  correct  map.  Position 
sketches  are  of  importance  to  show  unmapped  areas  of  prospective 
battle  fields,  camp  sites,  etc.,  and  may  thus  be  of  great  military 
value  to  a  commander. 

In  making  a  position  sketch,  the  first  endeavor  is  to  plot  on 
the  paper  the  locations  of  prominent  lines  and  points  of  possible 
military  value  such  as  railroads,  roads,  long  fences,  important 
streams  and  water  courses,  spires,  woods,  houses,  prominent  hill 
tops,  and  sometimes  single  trees  which  might  help  to  locate 
important  ground  forms  or  topography  near  them. 

These  lines,  points  and  features  are  located  by  base  line 
methods  and  by  traversing.  A  base  line  is  a  traverse  (or  mea- 
sured course)  as  from  A  to  B,  (Plate  B)  on  which  are  two  or 
more  points  from  which  interesections  can  be  made  to  locate 
other  prominent  features.  Base  lines  and  traverses  are  measured 
by  striding  and  are  plotted  as  carefully  as  possible.  Base  lines 
need  not  be  in  one  straight  line,  necessarily,  but  with  an  irregular 
base  line  or  traverse  more  care  is  required  than  when  working 
from  a  single  straight  line. 

On  the  sketch  in  Plate  B,  the  forks  of  the  roads,  trees  at 
the  edge  of  the  timber,  and  the  bridge  have  been  located  by  inter- 
section from  the  base  line  A-B.  The  line  A-B  was  selected  be- 
cause points  A  and  B  locate  important  ground,  also  the  distance 
A-B  could  be  measured  by  striding,  and  because  other  points  and 
lines  could  be  located  from  A  and  B  or  from  points  on  the  line 
A-B. 

To  locate  other  points  or  lines,  as  the  bank  of  the  stream  to 
the  northeast,  draw  a  ray  or  line  toward  the  bank.  The  distance 
may  be  obtained  by  counting  the  strides  to  that  point. 


24  Elements  of  Military  Sketching. 

The  points  and  lines,  referred  to  above,  when  plotted  on  the 
paper,  given  a  network  for  the  sketch  called  ''control,"  over  the 
area.  After  this  control  is  obtained,  the  topography,  that  is,  the 
contours  for  ground  forms,  the  cultivation,  small  ravines,  trees, 
houses,  etc.  can  be  filled  in  rapidly  because  each  such  feature  is 
near  a  point  or  line  already  located  on  the  sketch. 

Sometimes  sketchers  fill  in  the  topography  near  each  point, 
while  oriented  at  that  point,  before  proceeding  further. 

The  elevation  of  the  base  line  is  known  or  assumed  and 
slopes  having  been  determined  by  slope  board  or  hand  level,  the 
contours  for  the  ground  form  may  be  plotted  directly,  or  the 
degrees  of  slope  to  intersected  points  may  be  indicated  on  rays 
to  those  points,  (control)  and  the  contours  plotted  as  described 
in  paragraph  17. 

19.  A  theoretical  knowledge  of  sketching  will  not,  without 
considerable  practical  application,  make  one  a  proficient  sketcher. 
Military  sketches  to  be  of  value  must  usually  be  made  rapidly 
and  with  reasonable  accuracy.  In  road  sketching,  for  example, 
the  sketcher  would  generally  be  with  the  independent  cavalry, 
and  must  keep  up  with  it  from  day  to  day,  sending  back  the 
completed  road  sketch  each  night.  Experience  will  show  the 
sketcher  a  way  to  many  short  cuts;  for  example,  estimating  the 
slope  (or  number  of  contours)  between  points,  estimating  dis- 
tance to  features  off  the  road,  skill  in  rapid  orientation  and  actual 
drawing,  and  an  "eye  for  ground"  in  contouring. 


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